General Tolerances for Length Dimensions

General tolerances for length dimensions are defined in ISO 2768-1:1989. They apply to all linear dimensions—such as lengths, widths, heights, diameters, and radii—when individual tolerances are not specified on the drawing. This makes drawings clearer and manufacturing more consistent.

The standard divides tolerances into four accuracy classes: f (fine), m (medium), c (coarse), and v (very coarse). The selected class depends on how precise the dimension needs to be. For small dimensions, the permitted deviations are very small, while larger dimensions allow greater variation. This ensures that manufacturing remains practical and cost-effective.

For example, the designation ISO 2768-m on a drawing means that all length dimensions follow the medium accuracy class unless a specific dimension has been assigned a more precise tolerance.

General Tolerance Table for Length Dimensions

Tolerance class		Permitted deviations for nominal dimension ranges
Symbol	Description	>	0.5	3	6	30	120	400	1000	2000
		≤	3	6	30	120	400	1000	2000	4000
f	fine		0.05	0.05	0.1	0.15	0.2	0.3	0.5	-
m	medium		0.1	0.1	0.2	0.3	0.5	0.8	1.2	2
c	coarse		0.2	0.3	0.5	0.8	1.2	2	3	4
v	very coarse		-	0.5	1	1.5	2.5	4	6	8

The values in the table are given in millimeters (mm)